Re: [PATCH v7 0/5] Free the 2nd vmemmap page associated with each HugeTLB page

[Andrew Morton]

On Mon, 22 Nov 2021 12:21:32 +0800 Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:

> On Wed, Nov 10, 2021 at 2:18 PM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
> >
> > On Tue, Nov 9, 2021 at 3:33 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
> > >
> > > On 11/8/21 12:16 AM, Muchun Song wrote:
> > > > On Mon, Nov 1, 2021 at 11:22 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
> > > >>
> > > >> This series can minimize the overhead of struct page for 2MB HugeTLB pages
> > > >> significantly. It further reduces the overhead of struct page by 12.5% for
> > > >> a 2MB HugeTLB compared to the previous approach, which means 2GB per 1TB
> > > >> HugeTLB. It is a nice gain. Comments and reviews are welcome. Thanks.
> > > >>
> > > >
> > > > Hi,
> > > >
> > > > Ping guys. Does anyone have any comments or suggestions
> > > > on this series?
> > > >
> > > > Thanks.
> > > >
> > >
> > > I did look over the series earlier.  I have no issue with the hugetlb and
> > > vmemmap modifications as they are enhancements to the existing
> > > optimizations.  My primary concern is the (small) increased overhead
> > > for the helpers as outlined in your cover letter.  Since these helpers
> > > are not limited to hugetlb and used throughout the kernel, I would
> > > really like to get comments from others with a better understanding of
> > > the potential impact.
> >
> > Thanks Mike. I'd like to hear others' comments about this as well.
> > From my point of view, maybe the (small) overhead is acceptable
> > since it only affects the head page, however Matthew Wilcox's folio
> > series could reduce this situation as well.

I think Mike was inviting you to run some tests to quantify the
overhead ;)

> Ping guys.
> 
> Hi Andrew,
> 
> Do you have any suggestions on this series to move it on?
> 

I tossed it in there for some testing but yes please, additional
reviewing?